Foundry composition containing furfuryl alcohol polymer, foundry structure thereof, and method of making same



United States Patent FGUNDRY QQMPKDEEHTHQN CUNTAENHNG FUR- ]FURYLALCUHUIL POLYMER, FOUNDRY STRUG THEREQF, AND METHOD 6F MAKING M dStephen E. Freeman, Thiensyille, Wis, and John teiner,

tChicago, llll., assignors to Freeman Chemical Corporation, PortWashington, Wis a corporation of Delaware No Drawing. Filed June 27,1960, Ser. No. 38,715

12 Claims. (Cl. 260-41) This invention relates to essentially solid,shapeable, hardenable foundry mixes comprising particulate refractoryfoundry material and a stable, heat curable binder containing a curablefurfuryl alcohol polymer component and boron-containing component, hardfoundry structures that are produced from said foundry mixes, andmethods of producing said hardened foundry structures.

This application is a continuation-in-part of our allowed copendingapplication Serial No. 614,817, filed October 9, 1956.

More specifically, this invention relates to essentially solid,shapeable, hardenable, foundry mixes which comprise about 9l99.5% byweight of refractory foundry material (based on the weight of the entirefoundry mix), and about 0.5-6% by weight of a heat curable resinousbinder (based on the weight of the entire foundry mix) containing astable, heat curable binder having about -45% by weight curable furfurylalcohol polymer component (based on the weight of the entire foundrymix) and at least about 1% by weight boron-containing component (basedon the weight of the furfuryl alcohol polymer component). The stable,heat curable binder is stable at temperatures of up to at least about125 F. Further, this invention relates to foundry structures producedfrom the hardenable mixes, against which molten metal may be pouredwithout having the structures collapse or become distorted to thesetting or freezing of the metal. Still further, this invention relatesto methods of forming said hard foundry structures comprising heatingthe hardenable foundry mixes to about ISO-500 F.

If desired, other resinous binders, such as ureaformaldehyde resins, maybe used in conjunction with the stable, heat curable resinous binder offurfuryl alcohol polymer component and boron-containing component.However, the foundry mix must not contain more than a total of about 6%by weight resinous binder based on the total weight of the entirefoundry mix.

Our invention contemplates the use of stable, heat curable reactionproducts that may be used as heat curable binders for particulaterefractory foundry material to form foundry structures such as cores.These curable binders contain a curable furfuryl alcohol polymercomponent and a boron-containing component or reaction modifier. Thecurable binders are stable at normal storage temperatures, producefoundry cores having sufiicient green strength for some foundrypurposes, are capable of rapid curing in the presence of refractoryfoundry mate rial at moderately elevated temperatures, and may be usedto produce foundry cores having high tensile strength and scratchhardness values. The cores that are formed with these curable binderspossess sufficient porosity to permit the satisfactory escape of gasesformed during the casting operation. In addition the binder permits thecore structure to collapse after molten metal is poured against it andafter the metal has assumed its proper shape.

The moderately elevated curing temperatures of our curable bindersshorten the oven curing time or baking cycle when they are substitutedfor conventional linseed oil binders. These moderately elevated curingtemperatures permit shaped mixtures of refractory foundry material andcurable binder to be economically heated or cured in dielectric ovensand, in cases of relatively thin cores, in infrared ovens. However, theuse of dielectric ovens is generally restricted to cores that containwater or green strength binders such as a mixture of ceral and Water. Inconventional core binders which contain cereals or silicates, there is adecided loss in tensile strength and scratch hardness when the curedcores are stored in humid atmospheres. However, a baked core containingour cured binder may be stored for comparatively long periods withoutdeterioration.

Still further, when our curable binder is mixed with refractory foundrymaterial and formed into shell molds which are cured at moderatelyelevated temperatures and used to case high temperature molten metals(e.g., steel), the resulting molds have many advantages over thephenolic resins presently being used. For example, lower levels of ourcurable binder may be used to satisfactorily bond the refractory foundrymaterial.

Foundry cores may be produced with our curable binder by a method whichcomprises mixing or mulling particulate refractory foundry material witha binding proportion of a curable binder containing desired proportionsof a curable furfuryl alcohol polymer component and a boron-containingcomponent whereby a shapeable foundry mix is produced, forming a shapedcore from the mix that may be suitably hardened at moderately elevatedtemperatures, and curing the curable binder and refractory material atan elevated temperature so as to harden sufficiently the mix and producea foundry core.

The curable furfuryl alcohol polymer component and boron-containingcomponent may be added separately to the refractory material to form afoundry core mix or they may be premixed and added to the refractoryfoundry material as a mixture. Therefore, reference herein to the use ofthe curable binder in combination with the refractory foundry materialis intended to infer that components of the curable furfuryl alcoholpolymer component and refractory foundry material may be incorporatedinto the mix (i.e., refractory foundry material, and curable combinationof furfuryl alcohol polymer component and boron-containing component)separately or as an admixture. In either case, the curable polymer andrefractory components will be present in the foundry core mix as acurable mixture. For purpose of this invention, the relative proportionof curable furfuryl alcohol polymer component to boron-containingcomponent is not influenced by the manner in which they are added to therefractory material.

The phrases refractory foundry material, refractory material, refractoryfoundry core material and refractory foundry sand material are intendedto refer to unused and/or reclaimed, non-deleterious, refractory foundrymaterial that may be mulled with a binding proportion of the curablebinder to form a mix that may be shaped after the mulling step and thenhardened sufiiciently so as to produce a core or foundry structurehaving satisfactory tensile strength value. Thus, these phrases areintended to include conventional washed refractory foundry materials,such as exemplified by washed crude alumina, silicas, and clays. Forexample, zircon sands, Ottawa sand, and Mississippi sand from Rockford,Illinois, produce satisfactory foundry cores. In addition, these phrasesrefer to refractory foundry material that may include other foundryingredients, such as exemplified by iron oxide and various forms ofcarbon such as seacoal. The refractory foundry material should be freeof deleterious materials which interfere with the curing of the curablemixture of curable binder and refractory foundry material.

The curable furfuryl alcohol polymer component is herein intended torefer to partially polymerized furfuryl alcohol, polymerizable furfurylalcohol-containing resin complexes or reaction products, or suit-ableadmixtures thereof, which are capable of undergoing polymerization orcondensation-type reactions, herein referred to as curing, with theboron-containing component in the presence of refractory material atabout 180500 F., preferably about 200-400" F., so as to effectively anduniformly harden the refractory foundry material into a foundry core orstructure having satisfactory tensile strength. This term is notintended to exclude the presence of minor, non-deleterious proportionsof furfuryl alcohol monomer and/ or reaction product impurities orcomponents in the curable furfuryl alcohol polymer component as a partthereof; a minor proportion of the monomer serves as an extender for thepartial polymer and cures at elevated temperatures inthe presence of theboron-containing component.

It has been observed that in cases wherein the curable furfuryl alcoholpolymer component contains furfuryl alcohol monomer, a portion of themonomer volatilized from the refractory foundry material-curable bindermix during curing at moderately elevated temperatures, as indicated bythe odor emitted from the mix; the remaining portion of monomer cured inthe presence of or with the boroncontaining and refractory foundrymaterial and served as a binder. As the relative proportion of monomerto polymer is increased in the curable furfuryl alcohol polymercomponent, the resulting increased loss of potential binding propertiesmay be compensated for by increasing the proportion of curable binder(i.e., curable reaction mixture of furfuryl alcohol polymer componentand boron-containing component) to refractory foundry material so as toprovide an additional amount of partial polymer as well as monomer. Theherein described and claimed heat curable binder is intended to relateto admixtures wherein the partial polymer constitutes all or at least amajor or predominate portion thereof, and the monomer is present, if atall, in minor proportions (i.e., less than 50% by weight of the curablefurfuryl alcohol polymer component) only.

We have observed that as the relative proportion of monomer to partialpolymer is increased in the curable furfuryl alcohol polymer component,the curable binder (i.e., curable furfuryl alcohol polymer componentplus boron-containing component) should likewise be increased in orderto produce cured cores having high tensile strength values. For example,the curable mixture may consist of about 30 parts by weight of boricacid, 52 parts by weight curable furfuryl alcohol partial polymer, and48 parts by weight furfuryl alcohol monomer in order to produce a curedcore having a tensile strength equivalent to that produced by a curablemixture consisting of pants by weight of boric acid and 100 parts byweight of partial polymer.

The following curable furfuryl alcohol polymer components exemplify someof commercial products that may be used in accordance with ourinvention: furfuryl alcohol-phenolformaldehyde resins such as Durez14363, distributed by Durez Plastics Division of Hooker ElectrochemicalCo.; furfuryl alcohol-formaldehyde resins such as Varcum 8250,distributed by Varcum Chemical Corporation, and Quaker Oats Resin199-153, distributed by Quaker Oats Co.; and a monomer-free furfurylalcohol polymer such as Quaker Oats Resin 220-73 distributed by QuakerOats Co.

A suitable curable furfuryl alcohol polymer component may be preparedfor use in our curable mix by reacting furfuryl alcohol in the presenceof an acid or proton donor, for example, strong acids at lowtemperatures, or dilute solutions of strong acids, or weak acids atelevated temperatures. This reaction leads to polymerization orcondensation identifiable by an increase in molecular weight of thefurfuryl alcohol and readily observable by a darkening in color andgradual increase in viscosity.

The exothermic nature of this type of furfuryl alcohol polymerizationnecessitates careful control of reaction conditions, and the exercise ofcaution. Where an exotherm raises the temperature too rapidly,undesirable secondary reactions may ensue leading to unwanted products,or the reaction may accelerate beyond the scope of control so as toreact violently or to explode, thus rupturing the reaction vessel andfilling it with a hard, infusible resinous mass. In the last stages of arunaway polymerization, the temperature may rise hundreds of degreeswithin moments and, simultaneously, vast quantities of gas may begenerated.

The furfuryl alcohol polymer component may be made by a batch processsuch as set forth in Example 1, infra, or a continuous process such asexemplified by the procedure described in Example 1 of US. Patent No.2,570,027.

The terms boron-containing component and boroncontaining reactionmodifier herein refer to boron-containing materials that are free of aninterfering moiety, ion, or substance, and when admixed with thefurfuryl alcohol polymer component, with or without the presence ofrefractory foundrymaterial, forms a stable, heat curable foundry binderthat when admixed with a major proportion (i.e., at least about 91% byweight based on the entire foundry mix) of refractory foundry material,forms a foundry mix that is benign at room temperature but hardens intoa hard, self-supporting foundry structure at temperatures of about180-500 F.

The following boron-containing component exemplify some of the materialswhich may be used in accordance with our invention: boric oxide; boricacids or hydrates of boric oxide; certain boron esters such as ammoniumborate, sodium pentaborate, and boron acetate; and bo on complexes suchas diorthotolyl guanidine salt of dicatechol borate.

However, the presence of alkalies or predominantly alkaline ions in theboron-containing component tend to interfere with our reactionmechanism; thus, decidedly alkaline borates (e.g., sodium meta or tetraborate) may not be used in accordance with our invention unless theiralkalinity is reduced by the addition of acidulous material. In caseswhere the alkali is volatile (e.g., ammonium salts such as ammoniumborate), the ne ation may remain only until the alkali is volatilized.Alkaline borates of intermediate alkalinity (i.e., a pH of about 7-8),have some curing activity but in order to effect relatively rapidcuring, acidulous material must be added to the mulled mix; for example,10 parts by weight of sodium pentaborate and parts by weight of thepolymer produced in accordance with Example 1, infra, yieldedperceptible improvement in curing rate, although the presence of addedacidulous material would induce still more rapid curing.

In addition, when anions or other materials are present in theboron-containing component which materially remove the borate fromsolution (e.g., by an insolubilizing action), effective amounts of theborate will not be present to undergo effective curing with the furfurylalcohol polymer component. For example, lead ions tend to form insolublelead borate-which is not suitable for our purposes.

Furthermore, certain borate esters which consist of a preponderance ofnon-borate moiety (e.g., trioleyol borate and tricresyl borate) havebeen found not to be satisfactory because they do not permit thefurfuryl alcohol polymer component to undergo efifective curing. Thenon-borate moiety may interfere with effective curing due, possibly, toits plasticizing action on polymers formed during curing, or to sterichindrance.

If decidedly alkaline salts of borates are neutralized, such as wouldresult from the addition of acids, acidulous refactory material, ornon-metallic oxides thereto, they may be used in accordance with ourinvention. On the other hand, the high activity of acidicboron-containing 6 components may be reduced Where alkaline substancessuch as certain alkaline clays, alkaline metallic oxides, and the like,are present in the refractory foundry material; as the acidity of theboron-containing component and/ or refractory foundry material isincreased, the resulting increase in the curing rate may require carefulcontrol of the reaction mixture,

The boron-containing component enables lower boiling fractions of thecurable furfuryl alcohol polymer component to be cured below theirrespective volatilization points, thus enabling a greater mass of thecurable furfuryl alcohol polymer component to be cured and the resultinghardened core or foundry structure to possess higher tensile strengthand scratch hardness values. As the relative proportion ofboron-containing component to curable furfuryl alcohol polymer componenti increased in the heat curable binder, there is a tendency for thecured or hardened core to collapse more readily in the presence ofmolten metal at a given temperature. Furthermore, the boron-containingcomponent has the outstanding characteristic of being capable of beingmixed with the curable furfuryl alcohol polymer component so as toproduce a heat curable binder that is stable at conventional storagetemperatures and yet curable at moderately elevated temperatures.

When the boron-containing component is highly soluble in the curablefurfuryl alcohol polymer component (e.g., boric acid, boric oxide,ammonium borate, or certain borate esters), the reaction mixture orbinder ultimately becomes a homogeneous solution when moderatelyelevated curing temperatures are reached; as a consequence of thissolubility, uniform curing and a more homogeneous reaction productresults.

We have noted that boron-containing compounds and complexes contemplatedby our invention serve to reduce the time required to cure, at aboutl80-500 F., the curable furfuryl alcohol polymer component in admixturewith the refractory foundry material. That is, the time required to curea given curable furfuryl alcohol polymer component at a selectedconcentration (i.e., ratio of curable furfuryl alcohol polymer componentto refractory foundry material) may be reduced 10% and more (as measuredby the development of tensile strength), with our boron-containingcomponent.

The term stable, when used With respect to the stable, heat curablebinder, is herein intended to refer to a heat curable binder or reactionmixture which contains a furfuryl alcohol polymer component andboron-containing component and that is benign at temperatures up to atleast about 125 F. and may be admixed with particulate refractoryfoundry material and then heated at temperatures of about 180-500 F. toform a hard, selfsupporting foundry structure. The stable, heat curablebinder includes reaction mixtures of furfuryl alcohol polymer componentand boron-containing component that may be stored in a sealed containerfor at least 48 hours at temperatures up to at least about 125 F.Without losing their usefulness as an effective foundry binder, althoughthere might be some increase in their viscosity and some small tendencyfor them to develop gel particles, On the other hand, the stable bindermay retain its stability in a sealed container for many months, or evena year or more, at 70 F.

The composition of various suitable furfuryl alcohol polymer componentsand boron-containing components vary (for example, the furfuryl alcoholpolymer component may contain a minor proportion of a fur-furyl alcoholmonomer and/or impurities or components); therefore, the minimumproportion of boron-containing component that may be effectively used(in the heat curable binder) with the furfuryl alcohol polymer componentcannot be stated with exact precision. Generally, curable furfurylalcohol polymer component-boroncontaining component binders containingas low as about 1% by Weight of boron-containing component, based on theweight of furfuryl alcohol polymer component, produces a significantimprovement in the curing rate of the core.

For example, When boric acid is used, the stable, heat curable bindermay contain as low as about 2 /2% by Weight of boric acid with about 97/2% by Weight of the furfuryl alcohol polymer component (produced by themethod set forth in Example 1, infra), and as high as equal parts byWeight of boric acid and said polymer. When more than equal proportionsof boric acid to furfuryl alcohol polymer component are used, noappreciable advantage is realized in regard to the curing of the binder,although other desired effects which do not effect binding may beobtained. Therefore, the levels of curable binder (i.e., curablefurfuryl alcohol component plus boroncontaining component) hereinspecified are intended to in fer that additional boron-containingcomponent, but not curable furfuryl alcohol component, may be present inthe foundry mix or structure and that this added amount is, however, notessential to the forming of a satisfactory refractory binder and foundrystructure. We prefer to use in our curable mixture 10-30% by Weight ofboric acid and 70% by Weight of a furfuryl alcohol polymer componentsuch as produced by Example 1, infra. In the event that a proton donorcatalyst, such as hypophosphorus acid, is used in conjunction with ourcurable mixture or binder, comparatively lower proportions of boric acidto furfuryl alcohol polymer component may be used.

When boric oxide is used, the curable binder may contain as low as about2 /2 by Weight of boric oxide with about 97 /2% by Weight of the polymerproduced by the method set forth in Example 1, and, if desired, as muchas 15% by Weight boric oxide may be used with 85% by Weight of saidpolymer. We prefer to use 620% by weight boric oxide with 9480% byWeight of a furfuiyl alcohol polymer such as produced by Example 1.

A sufficient amount of curable mixture should be mulled with therefractory foundry material so as to permit the binder to intimatelycoat the refractory material. For example, mixes containing as low asabout 1-3 parts by weight of curable binder for each parts by Weight ofrefractory foundry material have been found to be sufficient for mostfoundry purposes; thus, a mix containing 1% by Weight of a curablebinder consisting of boric acid and furfuryl alcohol polymer may be usedwith 99% by weight of refractory foundry material. The upper limit ofthe relative proportion of curable binder to refractory foundry materialshould always be sufficiently loW so as to enable the cured core to havesulficient porosity and possess desirable collapse properties.

If desired, cereal (e.g., corn flour) and water may be incorporated intothe refractory foundry material heat curable binder mix in order to givethe mulled mix green strength properties. These green strength bindersmay also permit the use of lower proportions of the curable furfurylalcohol polymer component in the curable mixture of binder andrefractory foundry material. For example, one part by weight cereal and2.5-3 parts by Weight water may be added to 100 parts by Weight ofrefractory foundry material, and a desired proportion ofboron-containing component and about 0.5 part and above, by Weight, offurfuryl alcohol polymer may be added to a mulled mix containing thecereal, water, and refractory foundry material.

When Water is present in the mulled core mix, higher proportions ofboron-containing component to furfuryl alcohol polymer component ascompared to a Water-free mix, have been found to be advantageous. Asstated above, We prefer to use 1030% and 620% by Weight of boric acidand boric oxide, respectively, with the polymer produced in accordancewith Example 1; When Water is present in the core mix, the upper portionof these ranges are preferred.

In producing foundry cores in accordance with our invention, the curablebinder is mulled with refractory foundry material, the resulting mix isshaped, and the shaped mix is heated to about ISO-500 F., preferablyabout 200400 F., so as to produce a core having the desired properties.

We have found that when the curable binder and refractory foundrymaterial are mulled and then heated below about 180 F., the curingreaction is too slow for conventional foundry purposes. However, atabout 200 F curing of the curable binder and hardening of the coreoccurs at a satisfactory rate and the hardened or cured core willpossess excellent foundry core properties. As temperatures above about200 F. are used, the curing temperature and curing time should becorrelated so as to obtain maximum binding of the refractory foundrymaterial and produce a core having desirable collapsibility andcompressibility properties when in contact with the poured molten metal.

Curing conditions (i.e., time and temperature) which produceundercuring, produce soft cores having lower scratch hardness andtensile strength values. On the other hand, curing conditions whichproduce overcuring, produce cores which have passed their maximumscratch hardness and tensile strength values. In etfect, overcuring maybe regarded as destroying binding properties at a somewhat lowertemperature and rate than is normally effected by contacting the corewith molten metal. The destruction of binding properties by heat isreferred to as collapse. Thus, the curing temperature and the timeallowed for curing should be correlated so as to produce a core havingthe desired tensile strength. In some cases, it may be desirable toproduce cores having less than their maximum potential or obtainabletensile strength for given amounts of furfuryl alcohol polymer componentand boron-containing component because of the economies which resultfrom the use of less time and/or lower curing temperatures.

Linseed oil may be incorporated into the core mix as an extender for thecurable binder, but when used, the core generally requires the use of ahigher curing temperature and/or longer period of curing.

In producing foundry cores in accordance with our invention, thefurfuryl alcohol polymer component and boron-containing component may bepremixed so as to produce the curable binder. The binder is then mulledwith the refractory material until an intimate admixture of thesematerials is obtained. The mulled mix may then be placed into core boxeswith air blowing, or slinging or conventional hand-packing methods. Ifdesired, the filled core box may be jolted or its contents may be rammedso as to assure dense and complete filling of the confines of the corebox.

In the event that the refractory foundry material and binder mix isincapable of maintaining its shape without support, hot gas or air maybe blown through the mix prior to the removal of the mix from the corebox in order to produce sufiicient hardening of the core, or, asalternative procedures, the filled core box may be heated in an oven ora hot core box may be used.

If the core possesses suflicient green strength so as to be capable ofmaintaining its shape without the support of the box, the mix may beremoved from the box and hardened in an oven; as an alternativeprocedure, the core box itself may be heated to effect the final cure ofthe mix.

After the mix is cured, the hardened core may be used for shaping moltenferrous metals, cuprous metals, zinc, and aluminum. For example,excellent castings are produced by pouring molten iron at about 2900 F.into molds containing our cured cores; the collapse rate of the core andthe surface finish of the casting will be of a superior nature. Othermetals having relatively low melting temperatures, such as 12001500 F.,may be poured around the core depending upon the collapse requirementfor the core. Where a slowly collapsing core is required for low meltingmetals, our curable heat binders may possess satisfactory collapseproperties when properly controlled proportions of boron-containingcomponent are used.

Our heat curable binders may also be used in so-called shell moldprocesses whenever conditions so permit. A typical phenol-formaldehyderesin commonly used in shell molding permits the formation of aself-sustaining coating at about 350 F. and requires the additionalheating of the pattern and adherent coating to about 550 F. in order toeffect the ultimate curing of the mix; our curable binder may be curedto bind refractory foundry sand material in a like manner at the same orlower temperatures.

EXAMPLE 1 The following procedure may be used to produce a suitablefurfuryl alcohol polymer component: Warm 2,997 lbs. of furfuryl alcohol,while stirring, in a 1,200 gallon gross capacity, stainless steel,heated (about 180 F.), closed reaction kettle equipped with refluxcondenser, agitator, jacket for Water-cooling, and gas-fired Salasburners automatically set to about 180 F. Add, gradually 169.7 lbs. of a2% aqueous solution of commercial phosphoric acid in 10 pound incrementsabout 5 minutes apart, adding additional 10 pound increments as anyexotherm is dissipated; this operation usually consumes about 1 /2hours. Continue stirring and observing the reaction mixture for 10 to 15minutes in order to be certain that the temperature will drop when heatis removed and that no exotherm will occur; then add a second unit of84.8 lbs. of 2% phosphoric acid in 10 pound increments, as before, overa period of 45 to 60 minutes, depending on the time required todissipate the heat. After a second holding period of 10 to 15 minutesand assurance that exothermic heat has subsided, again add,incrementally, another 84.9 lbs. of acid in a period of 45 to 60minutes.

If at any time an exotherm is observed, maintain the temperature of thecontents of the reaction vessel at F. by admitting a sutficient quantityof cold water. If no exotherm occurs after the final addition of thelast unit of acid, the temperature of the reaction mixture should beraised slowly to refluxing temperature (i.e., 200-215 F.) and held atgentle reflux until a milky appearance occurs at a viscosity of A to B(Gardner- Holdt scale); controls should be run every 5 minutes until Ito L viscosity is reached. Water may be removed by decantation orcentrifugation in order to obtain true viscosity values for the furfurylalcohol component. After a viscosity of about J to L is reached, heatshould be removed and the reaction mixture should be neutralized to a pHof 5 by the addition of about 30 lbs. of 10% by weight aqueous sodiumhydroxide.

EXAMPLE 2 Curable mixtures of only boric acid (i.e., H 80 and thefurfuryl alcohol polymer component produced in accordance with Example 1were prepared in the following proportions:

(a) 1 part by wt. boric acid 2 parts by wt. furfuryl alcohol polymercomponent (b) 1 part by wt. boric acid 4 parts by wt. furfuryl alcoholpolymer component (0) 1 part by wt. boric acid 9 parts by wt. furfurylalcohol polymer component (d) 1 part by wt. boric acid 19 parts by wt.furfuryl alcohol polymer component These curable binders were aged inseparate closed containers for fourteen days; no change in theirappearance occurred, except for a darkening of their surfaces. Othersamples of these curable mixtures which were stored for fifty daysshowed slight or insignificant loss of' binding properties withoutobservable additional Table II changes in color, except at theirsurfaces, and viscosity.

Parts Tensile strength (p.s.i.)

EXAMPLE 3 Parts Parts furfuryl 5 refrac- (boric acid) alcohol a Table I,infra, shows tensile strength data which were y (H1301) Polymer 200 R300 matenal 1 compocure (for cure (for obtamed by curing separatesamples of a mix conslstnent 1% hrs.) 1hr.) mg of refractory corematerial, furfuryl alcohol polymer component, and boric acid at 200 F.and 300 F. for 100 0.04 0.5 250 1 /2 hours and 1 hour, respectively. Thetable also shows 10 $8 8- 3 g- 2 5 that no significant or measurableloss of binding prop- 100 0:38 115 370 erties was noted after theuncured mulled mixtures were igg 8-2; gggg stored in closed containersfor 10 days. 100 1.25 2.5 300 The tensile strength data were obtained bypreparing standard tensile bars in accordance with standard Ameri- 1Ottawa (A.F.S. No.17) sand. can Foundry Society methods using DietertMachines to D2 Conlipgnent produced in accordance with the method setforth in xamp e k s' 1 n 32 tg g k i i z gg g ggg Z Z f i i Tables IIIand IV, infra, show tensile strengths which Wei p p were obtained byincorporating corn flour and water into g various refractory mixes. Thetensile strength data set Table I forth in these tables were obtained bypreparing standard tens1le bars 1n accordance with standard A.F.S.methods using Dietert Machines to form, temp, and break the PartsTensile strength (p.s.i.) bars. Curing was elfected in ovens. Parts bParts d fulrlifi'yil refracorie aci a co 0 A I" tory (11,1303 polymer200 F. 300 F. EX PLE 5 mammal gg? fig The data in Table III wereobtained by testing mixes which contained 100 parts by Weight of Ottawasand, 100 Q32 5 370 370 varying parts by weight of boric acid, varyingparts by 100 0. 03 2.5 300 370 weight of furfuryl alcohol polymercomponent produced 100 300 370 by the method of Example 1, one part byweight of corn E T Y M TERIAL BINDER flour, and 2.5 parts by weight ofwater. These data sug- OURED' R lla iii agi na IOADAYS ges'ts thatrelatively higher proportions of boric acid may be used in conjunctionwith the furfuryl alcohol polymer 100 0. a2 2.5 370 370 when moisture ispresent. 100 0. e3 2. 5 370 370 p 100 1.25 2. 5 370 370 Table III 1Ottawa (A.F.S. fineness No. 17) sand. Parts by 2 Component produced inaccordance with the method set forth in $353 g g g Example 40 Parts byweight Parts by alcohol Parts by Parts by (p.s.i.) refractory materialweigit of ploymer weight weight cores Refractory foundry material whichhad been mulled H3 $1, 5 35 com flour wate gi fi with the proportions ofboric acid and furfuryl alcohol E ple forlhr. polymer set forth in TableI was. found to be useful after being stored in closed containers for asmuch as: 6 weeks;

.1 .5 1 the resulting loss of tensile strength was found to be un- 2,2 00 2 Low Do 0.3 0.5 1 2 5 270 important for most foundry purposes. 0' 5 Q5 1 2'5 230 0.25 1.0 1 2.5 EXAMPLE 4 0.5 1.0 1 2.5 375 it it 1 185 Thetenslle strength data set forth in Table II, infra, 50 were obtained inthe same manner as described in Ex- PL 6 ample 2, supra, w1th variousspeclfied proportlons of bor1c EXAM E acid and furfuryl alcohol polymer.The term parts in The data 1n Table IV, lnfra, show that refractorymate- Table II refers to parts by weight. rial which contains reclaimedsand or a mixture of unused Table IV Parts by Tensile strength (p.s.l.)weight of Parts by curable Parts by weight of mixture of Parts by Partsby Cured at 300 F. Cured at 350-400 F. weight of reclaimed equal partsweight of weight of afteraitcr lake sand lake sand by weight water cornflour of polymer of Example 1 hr. 1% hrs. hr. 1% hrs and 11 as well asreclaimed refractory foundry material may be used to producesatisfactory foundry cores with our curable mixtures. Three hundred andseventy was the highest reading that could be determined with thetensiletesting machine used in obtaining tensile strength values; thetensile strength values set forth in brackets were obtained byinterpolation.

The data in Table IV, supra, show unexpectedly low tensile values forcures at 350-400 F. In the absence of green strength binders such aswater plus cereal, cures within this temperature range produce coreswith comparatively higher tensile values which are maintained forcomparatively long periods of time.

We have found that an admixture of furfuryl alcohol monomer plus aboron-containing component such as boric acid serves as a parting-agentor lubricant for facilitating removal of a shaped core from the corebox. It would appear that the high solubility of the sticky furfurylalcohol polymer component in the monomer portion of the parting-agentcauses a non-stocky, diluted layer to be formed on the walls of the corebox. In addition, this admixture does not introduce foreign matter intothe core, and, as a result of its use, the cured core may possessadditional surface hardness properties. However, when this parting-agentor lubricant is used, the amount of furfuryl alcohol monomer present inthe core should never exceed or equal that of the polymer.

The term consisting essentially of as used in the claims is intended toexclude the presence of unnamed materials in such amounts as tointerfere substantially with the properties and characteristicspossessed by the composition set forth but to include the presence ofother materials in such amounts as not substantially to affect saidproperties and characteristics adversely.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications will be obvious to those skilled in the art.

We claim:

1. An essentially solid, shapeable, hardenable, porous foundry mix whichcomprises: about 91-99.5% by weight refractory foundry sand material,based on the weight of the entire foundry mix, and about 0.5-6% byweight, based on the weight of the entire foundry mix, of a heat curableresinous binder containing a stable, heat curable binder having about-45% by weight of curable furfuryl alcohol polymer component, based onthe weight of the entire foundry mix, and at least about 1% by weight,based on the weight of the furfuryl alcohol polymer component, of aboron-containing component that provides, with the polymer component, astable binder at temperatures up to at least about 125 F., said mixsuitably hardening at about 180-500 into a hard, self-supporting, porousfoundry structure against which molten metal may be poured and shaped.

2. The foundry mix of claim 1 wherein said boroncontaining componentcontains a member of the group consisting of =boric oxide and hydratesof boric oxide.

3. An essentially solid, hard, porous foundry structure against whichmolten metal may be poured before said structure undergoes distortion orcollapses, which comprises: about 91-99.5% by weight refractory foundrysand material, based on the weight of the entire foundry structure,bonded with about 0.56% by weight, based on the weight of the entirefoundry structure, of a polymerized reaction product produced by mixingand then heat ing an admixture of said refractory material and a heatcurable resinous binder at about l8050() F., said heat curable resinousbinder containing a stable, heat curable binder having about 0.54% byweight of curable furfuryl alcohol polymer component, based on theweight of the entire foundry mix, and at least about 1% by weight, basedon the weight of the furfuryl alcohol polymer component, of aboron-containing component that provides, with the polymer component, abinder that is stable at temperatures up to at least about F.

4. The foundry structure of claim 3 wherein said boroncontainingcomponent contains a member of the group consisting of boric oxide andhydrates of boric oxide.

5. A method of producing a hardened foundry structure for shaping moltenmetal comprising: mulling an essentially solid, hardenable foundry mixcontaining about 91-99.5% by weight refractory foundry sand material,based on the weight of the entire foundry mix, about ().56% by Weight,based on the weight of the entire foundry mix, of heat curable resinousbinder containing a stable, heat curable binder having about 0.5-4.5% byWeight of curable furfuryl alcohol polymer component, based on theweight of the entire foundry structure, and at least about 1% by weight,based on the Weight of the furfuryl alcohol polymer component, of aboroncontaining component that provides, with the polymer component, astable binder at temperatures up to at least about 125 F., whereby ashapeable mix is formed, forming a self-supporting, shaped, porousfoundry mass which hardens at about -500" F., and curing the curablebinder in said shaped mass by heating said mass to at least about 180 F.to produce a hard, porous structure against which molten metal may bepoured and shaped without undergoing distortion or collapsing.

6. The method of claim 5 wherein said boron-containing componentcontains a member of the group consisting of boric oxide and hydrates ofboric oxide.

7. An essentially solid, shapeable, hardenable porous foundry mix whichconsists essentially of: a major proportion of refractory foundry sandmaterial and less than about 3.75% by weight, based on the weight of theentire foundry mix, of a stable, heat curable binder containing at leastabout 0.5% by weight curable furfuryl alcohol polymer component, basedon the Weight of the entire foundry mix, and at least about 1% byweight, based on the weight of the furfuryl alcohol polymer component,of a boron-containing component that provides a stable binder attemperatures up to at least about 125 F., said mix suitably hardening atabout ISO-500 F. into a hard, self-supporting, porous foundry structureagainst which molten metal may be poured and shaped before said hardenedstructure undergoes distortion or collapses.

8. The foundry mix of claim 7 wherein said boron-containing componentcontains a member of the group consisting of boric oxide and hydrates ofboric oxide.

9. An essentially solid, hard, porous foundry structure against whichmolten metal may be poured before said structure undergoes distortion orcollapses, which consists essentially of: a major proportion ofrefractory foundry sand material bonded with less than about 3.75% byweight, based on the weight of the entire foundry structure, of apolymerized reaction product produced by mixing and then heating anadmixture of said refractory material and a stable, heat curable binderat about 180- 500 F., said stable, heat curable binder containing atleast about 0.5% by weight curable furfuryl alcohol polymer component,based on the weight of entire foundry structure, and at least about 1 byweight, based on the weight of the furfuryl alcohol polymer component,of a boron-containing component that provides a stable binder attemperatures up to at least about 125 F.

10. The foundry structure of claim 9 wherein said boron-containingcomponent contains a member of the group consisting of boric oxide andhydrates of boric oxide.

11. A method of producing a hardened foundry structure for shapingmolten metal comprising: mulling an essentially solid, hardenablefoundry mix consisting essentially of a major proportion of refractoryfoundry sand material with less than about 3.75% by weight, based on theweight of the entire foundry mix, of a stable, heat curable bindercontaining at least about 0.5 by weight of curable furfuryl alcoholpolymer component, based on the Weight of the entire foundry mix, and atleast about 1% by weight, based on the Weight of the furfuryl alcoholpolymer component, of a boron-containing component that provides astable binder at temperatures up to at least about 125 F., whereby ashapeable mix is formed, forming a self-supporting, shaped, porousfoundry mass which hardens at about ISO-500 F and curing the curablebinder in said shaped mass by heating said mass to at least about 180 F.to produce a hard, porous structure against which molten metal may bepoured and shaped before said structure undergoes distortion orcollapses.

14 12. The method of claim 11 wherein said boron-containing componentcontains a member of the group consisting of boric oxide and hydrates ofboric oxide.

References Cited in the file of this patent UNITED STATES PATENTSStrigle et a1 Oct. 30, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,024,215 March 6, 1962 Stephen E. Freeman et a1.

he above numbered pat- It is hereby certified that error appears in tPatent should read as ent requiring correction and that the said Letterscorrected below.

Column 1, line 37, after "distorted" insert, prior column 2, line 6, for"ceral" read cereal column 10, lines 31 and 32, for "suggests" readsuggest Signed and sealed this 5th day of November 1963.

(SEAL) Anest:

EDWIN L. REYNOLDS ERNEST W. SWIDER Ac t i ng Commissioner of PatentsAttesting Officer

1. AN ESSENTIALLY SOLID, SHAPEABLE HARDENABLE POROUS FOUNDRY MIX WHICHCOMPRISES: ABOUT 91-99.5% BY WEIGHT REFRACTORY FOUNDRY SAND MATERIAL,BASED ON THE WEIGHT OF THE ENTIRE FOUNDRY MIX, AND ABOUT 0.5-6% BYWEIGHT BASED ON THE WEIGHT OF THE ENTIRE FOUNDRY MIX, OF A HEAT CURABLERESINOUS BINDER CONTAININIG A STABLE, HEAT CURABLE BINDER HAVING ABOUT0.5-4.5% BY WEIGHT OF CURABLE FURFURYL ALCHOL POLYMER COMPONENT, BASEDON THE WEIGHT OF THE ENTIRE FOUNDRY MIX, AND AT LEAST ABOUT 1% BY WEIGHTBASED ON THE WEIGHT OF THE FURFURYL ALCOHOL POLYMER COMPONENT, OF ABORON-CONTAINING COMPONENT THAT PROVIDES, WITH THE POLYMER COMPONENT, ASTABLE BINDER AT TEMPERATURES UP TO AT LEAST ABOUT 125* F., SAID MIXSUITABLY HARDENING AT ABOUT 180-500*F. INTO A HARD, SELF-SUPPORTING,POROUS FOUNDRY STRUCTURE AGAINST WHICH MOLTEN METAL MAY BE POURED ANDSHAPED.